Answer:
139.25 cm^2.
Explanation:
The bottom part of the opening is a square, so you just square the 10. Then, since it's a square, it's 10 horizontally too, making the bottom of the semicircle 10 cm. Based on that, you can get the radius (10 is the diameter pretty much, so 5) then use the typical formula to find a circles' area [(pi)r^2, which gets you 78.5 or so]. It's a semicircle though and that formula would give you the area if the circle was a full round one, so you just divide it by 2 (which should get you about 39.25).